Grinding mills



July 21, 1959 e. w. EDWARDS ETAL 2,895,689

GRINDING MILLS Filed April 19. 1956 United States Patent 2,895,689 GRINDING MILLS George Wilfred Edwards and Roger Joseph Sevin,

Paris, France Application April 19, 1956, Serial No. 579,225

Claims priority, application France April 20, 21955 4 Claims. (Cl. 241-223) This invention relates to grinding mills of the kind including a rotatable grinding wheel or disc.

On operation of grinding mills having cooperating grinding wheels or discs at least one of which is rotatable at high speed, the substance being treated between such Wheels or discs becomes heated. In certain cases it is necessary to limit this often harmful heating and to maintain the temperature as low as possible.

When the grinding wheels are made of a heat-conduct ing material, it is possible to eflect cooling by circulation of water or any other cooling liquid when however the grinding wheels are made of non-conductive material, or if the cooling surfaces are inadequate, the temperature cannot be lowered sufl'iciently and in such a case intense evaporation often occurs at the outlet from the grin-ding wheels where the hot material is ground or homogenised.

It is the chief object of the present invention to provide means whereby the material treated during the grinding operation may be cooled and loss of solvent by evaporation minimised.

According 'to one aspect the invention resides in a method of reducing the temperature of a product produced in a grinding mill incorporating cooperating grinding wheels or discs at least one of which is rotated at high speed such method consisting in circulating air or vapour in a closed circuit wherein such air or vapour will be caused. to pass over the product issuing from the grinding wheels or discs and will be subsequently cooled prior to re-passage'over said product.

According to a further aspect the invention resides in a method of reducing the temperature of a product produced in a grinding mill incorporating cooperating grinding wheels or discs at least one of which is rotated at high speed such method consisting in employing a volatile liquid as a heat transfer means between the product and a cooling medium, the vapour produced as a result of evaporation in the grinding zone being subsequently condensed and returned as liquid to the feed side of the mill or to some other point.

In accordance with yet a further aspect in a grinding mill wherein the heated product issuing from cooperating grinding wheels passes via a collecting space or compartment to an outlet there is provided a cooling system wherein a positive air or vapour flow is set up through said collecting space or compartment.

In order that the said invention may beclearly understood and readily carried into eifect the some will be hereinafter more fully described With reference to the accompanying drawing which shows a section through a grinding mill.

The grinding mill illustrated is of the type equipped with a high-speed grinding wheel and referring now to the drawing, 1 denotes a hearing which is capable of axial sliding movement within a casing 2.

In order to adjust the gap between the grinding wheels, the bearing is adapted to be moved axially with respect to the casing, this movement being imparted by means of a hand wheel 3 carrying two differential screw-threads one of which screws into the casing and the other on to the body of said bearing.

Screwed to and centred on a shaft 4 which is carried by the bearing 1, is a grinding wheel support hub 5 the latter carrying a plate 6 in which a grinding wheel 7 is supported.

The grinding wheel 7 which is rotatable as well as axially movable is mounted on a sleeve 8 and is located thereon by means of a nut -9 which carries vanes or wings 9'.

Thus the unit consisting of the grinding wheel 7, sleeve 8 and vane-carrying nut 9 is centred directly on the shaft 4 and bears against the plate 6. The said unit is locked in position by means of a nut 10.

11 denotes a stationary grinding wheel which is carried by and centred in a cover 12 fixed to the front of the casing 2. I

The product which is to be ground or homogenised is fed into a hopper 13 fixed to the cover 12.

On operation of the mill the product will be entrained by the vanes 9' on the nut 9 and will be sucked through the hopper and forced into the gap between the grinding wheels 7 and 11, the width of said gap being adjustable by means of the hand wheel 3.

When it passes between the grinding wheels, the product is spread out and is subjected to an intensive shearing eifect.

Upon issuing from the grinding wheels, the product is projected into a collecting chamber in the casing 2 and is finally evacuated through the channel 14. As the product passes between the grinding wheels, part of the work done will be transformed into heat. Moreover, as the product is ground evaporation will occur at the outlet from the grinding wheels, especially when the substance being treated contains volatile products.

The casing 2 of the apparatus is formed behind the collecting chamber with a secondary chamber 15 which is separated from the said collecting chamber by a partition 16. Mounted on that face of the plate 6 opposite the partition 16 are vanes 17 which when the grinding wheel 7 is rotating serve to produce an air flow which is drawn from the secondary chamber 15 and is expelled into the collecting chamber, to be finally evacuated through the channel 14.

A collecting vessel 18 is fitted to the channel 14 and such vessel which may or may not be cooled, comprises at its lower or outlet end a trap 19 in such manner that liquid can be discharged from said outlet without air or vapours escaping from the collecting vessel at the same point.

Connected to the upper part of the collecting vessel is a pipe 23 leading to a cooler 20 which in turn is connected by another pipe 24 to the secondary chamber 15 of the grinding mill. Thus there is a circulation of air or vapour in a closed circuit, which comprises{ The secondary chamber 15.

The collecting chamber.

The collecting vessel 18.

The cooler 20, and

Return to the secondary chamber 15.

again as it passes out of the grinding Wheels, and, following the same circuit, will be condensed again in the cooler, then re-introduced into the product being fed into the mill, and so forth.

At the time it is evaporated, the volatile liquid will take from the ambient medium ie from the product being treated, heat corresponding to its heat of evaporation, and thus there will be a corresponding lowering of temperature.

The heat taken from the product by the volatile liquid will thus be conveyed to the cooler and transmitted to the cooling water at the time the vapours are condensed.

It will therefore be seen that in the case of the aforesaid arrangement, the heat can be taken from the product being treated in the grinding mill, and dissipated by the water or any other cooling substance, through the intermediary of a volatile liquid already contained in the product or intentionally incorporated in the product.

By way of example, and without limiting theuse of this method, the case of grinding paint may be quoted.

A certain quantity of solvent compatible with the paint and having a boiling point equal to or less than the maximum permissible temperature, may be deliberately added to the paint.

It will be apparent from the foregoing that the arrangement according to the invention as described hereinbefore affords the double advantage of extracting heat from the product being treated and of minimising the escape of solvents or of noxious vapours to the outside, by providing a closed ventilation circuit within the apparatus.

We claim:

1. In the wet grinding of materials in a high speed grinding mill the method of cooling. the material being ground between the grinding elements of the mill comprising the steps of adding a volatile liquid to the material to be ground in the mill the boiling point of which is at least as low as the maximum permissible temperature to which the material being ground may be heated in the grinding operation, feeding the material containing the added volatile liquid to the mill and into contact with the grinding elements of the mill, absorbing the heatproduced in the grinding operation by the added volatile liquid to supply heat of vaporization thereof and vaporize the added volatile liquid during the grinding of the material by the grinding elements, thereby preventing the heating of the material being ground to a temperature above said permissible maximum temperature, projecting the ground material together with the vapors of the volatile liquid into a collection zone, and separately recovering the ground material and the vapors of. the vaporized volatile liquid.

2. In the wet grinding of materials in a grinding mill the method of cooling the material being ground between the grinding elements of the mill' including a high speed.

grinding wheel, comprising the steps of adding a volatile liquid to the material to be ground in the mill theboiling point of which is at least as low as the maximum permissible temperature to which the material being ground may be heated in the grinding operation, feeding the material containing the added volatile liquid to the mill and into contact with the grinding elements of the mill including the high speed grinding wheel, absorbing the heat produced in the grinding operation by the added volatile liquid to supply the heat of vaporization thereof and vaporiz ethe added volatile liquid during the grinding of the material by the grinding elements, thereby preventing the heating of the material being ground to a temperature above said permissible maximum temperature, projecting the ground material together with the vapors of the volatile liquid by the high speed grinding wheel into a collection zone surrounding the periphery of the grinding wheel, introducing a gaseous carrier meduced in the grinding operation in the mill, the grinding mill including a high-speed grinding wheel a grinding face of which adjacent its periphery cooperates with an adjacent grinding element, a hopper for holding a body of the material containing the volatile liquid, means for feeding the material containing the volatile liquid from the hopper along said wheel toward its periphery and between said face of the wheel and the grinding element, a collecting chamber surrounding the periphery of the wheel into which the ground material and vapors of the volatile liquid vaporized during the grinding operation are projected by the grinding wheel, a collecting vessel receivingv the ground material. and vapors from the collecting chamber, means for supplying a stream of gaseous carrier medium into the collecting chamber to mingle with the ground material and the released and projected vapors and carry them into the collecting vessel, means connected with the collecting vesselfor receiving and condensing the vapors ofthe volatile liquid, and means for conducting the resulting condensate to the hopper to mingle with the material therein.

4. Inan apparatus including a grinding mill for the wet grinding of materials containing a volatile liquid vaporizab'le at the temperature caused by the heat produced in the grinding operation in the mill, the grinding mill including a high speed grinding wheel a grinding face of which adjacentits periphery cooperates with an adjacent grinding element, means for feeding the material containing the volatile liquidalong said wheel toward its periphery and between said face of the wheel and the grinding element, a collecting chamber surrounding, the periphery of the wheel into which the ground material and vapors of the volatile liquid vaporized during the grinding operation are projected by the grinding wheel, a collecting vessel receiving the ground material and vapors from the collecting chamber, an annular passageway along the opposite face of the grinding wheel opening into the collecting chamber, impeller blades carried by the grinding wheel in said passageway and mounted so as to impel a stream of gaseouscarrier medium into the collecting chamber to mingle with the released projected vapors and carry them into the collecting. vessel, and means for supplying a stream of gaseouscarrier medium to said passageway.

References Cited in the file of this patent UNITED STATES PATENTS 1,762,241 Pontoppidan June 10, 1930 1,795,603 Hussey Mar. 10, 1931 1,847,967 Keefer Mar. 1, 1932 2,144,333 Hagen Ian. 17, 1939 2,184,903 Baehr Dec. 26, 1939 2,212,544 Lund Aug. 27, 1940 2,295,473 Hollstein Sept. 8, 1942 2,400,382. Arnold May 14, 1946 2,561,043 Ayers July 1-7, 1951 2,609,150 Bludeau Sept. 2, 1952 2,609,995 Klagbrunn Sept. 9, 1952 2,677,504 Klingel May 4, 1954 Y FOREIGN- PATENTS 287,318 Great. Britain Mar. 22, 1928 524,998' Great Britain Aug. 20. 1940 

